1. Field of the Invention
This invention relates to a filtering module comprising a bundle of microporous hollow fibers and a water purification device utilizing such a filtering module.
2. Prior Art
In recent years, city water has been much deteriorated. For example, such city water contains organic substances such as phthalic ester and also contains excessive alkali earth metal ions or the like. This is quite undesirable from the viewpoint of health and adversely affects the taste of the water. Also, it is important to secure drinking water in developing countries and disaster-striken areas. The drinking water in such countries and areas may contain infectious bacilli such as dysentery bacilli, cholera bacilli and typhoid bacilli as well as colon bacilli. Therefore, it has been desired to remove organic substances, taste-affecting substances and the various bacilli or bacteria from the drinking water.
There is known one conventional water purification or treatment device which utilizes activated carbon and is adapted to be connected to a faucet of city water to remove impurities and objectionable odor-developing substances from the water by adsorption. Another conventional water purification device utilizes an ion exchange resin column for softening hard water. A further conventional water purification device utilizes a reverse osmosis method. In the case of the water purification device utilizing activated carbon, the activated carbon absorbs chlorine serving as a sterilizing component in city water, and the water in the purification device loses its sterilizing effect. As a result, bacilli or bacteria tend to propagate in the water purification device so that they are introduced into the water passing through the water purification device.
The ion exchange resin is only effective in removing ions in the water and can not remove bacilli and nonionic impurities, and there is also the risk that bacilli or bacteria propagate in the water purification device.
The water purification device of the activated carbon type and the ion exchange resin column both require a pump or the like in order to purify the water. Therefore, the purified water can not easily be obtained at any place with these devices. Also, the reverse osmosis method requires a rather bulky equipment and a high pressure-generating means. Thus, the purified water can not also be easily obtained with this method.
There has also been proposed a handy or portable water purification device designed to treat water in a lake, a swamp, a pond or a river to obtain a drinking water in an emergency such as an earthquake and other disasters. In such a handy water purification device, water to be treated is first filtered by a filter of a relatively large pore size, and the filtered water is treated by activated carbon. Then the water is sterilized by sodium hypochloride or the like. However, the resultant water has the odor of the sterilizing agent and contains the organic substances passed through the filter. Therefore, the treated water is quite unsavory.
A further conventional water purification device comprises a tube containing activated carbon and having a membrane secured to one end thereof for preventing the passage of bacilli, and a hand-operated pump of the syringe type to cause water being purified to pass through the flat membrane. However, with such a hand-operated pump, the rate of permeation of the water through the membrane is not satisfactory. In addition, When air is introduced into the water to be purified, the permeation rate further becomes low.
In order to overcome the deficiencies of the above water purification devices, there has been proposed a water purification device which comprises a hollow fiber-filtering module, and activated carbon unit and an ion exchange resin unit. The conventional filtering module of the type which filters the whole of liquid introduced thereinto comprises a bundle of hollow fibers made of a hydrophilic membrane. When the liquid containing gas such as air is introduced into the filtering module through an inlet port thereof, the gas can not permeate the hollow fiber at a pressure, for example, of 1 kg/cm.sup.2 so that such entrapped gas will be disposed in contact with the outer surfaces of the hollow fibers. As a result, such entrapped gas will prevent the water from permeate the hollow fibers, so that the overall permeability of the hollow fiber bundle becomes lower.
In the case of the conventional filtering module of the type designed to filter part of the liquid introduced thereinto, the gas entrapped in the filtering module may be discharged therefrom together with those of the liquid which has not been filtered. In this case, there is the disadvantage that a relatively large amount of water must be treated to obtain some amount of purified water. In the case of the filtering module designed to filter the whole liquid, the entrapped gas can not be discharged from the filtering module, and therefore if a large amount of gas is entrapped in the filtering module, the liquid can hardly permeate the hollow fibers.
In order to overcome this difficulty, it has been proposed to degas the liquid before it is introduced into the hollow-fiber filtering module. However, this method requires a tank of a relatively large size and a vacuum pump and hence is rather expensive. Another alternative is to flow the liquid downwardly through the filtering module so that the gas contained in the liquid will collect in the upper portion of the filtering module. This method is not entirely satisfactory, however, in that when a large amount of gas is introduced into the filtering module, the filtering efficiency of the hollow fibers is still adversely affected. A further proposal is to provide a gas reservoir with a vent cock adjacent to an upper inlet port of the filtering module so that the gas entrapped in the gas reservoir can be discharged by manipulating the vent cock. With this method, if the gas reservoir of a large size is provided, the overall size of the filtering module is increased, and a dead space is also increased. On the other hand, if the gas reservoir is kept to a small size, the vent cock must be frequently manipulated. Also, care must be always taken of the amount of water to be filtered so that gas is not inadvertently introduced into the filtering module.